Comparison of grain dehydration and mechanical harvest quality between spring-sown maize and summer-sown maize in the middle reaches of Yangtze River

【Objective】To clarify the differences in mechanical harvest quality and grain dehydration dynamics between spring-sown maize(SP) and summer-sown maize(SM) and the influencing factors, provide reference for matching planting modeand agronomic measures for mechanical harvest of double-cropping maize in the middle reaches of Yangtze River.【Method】Three main local maize varieties, including Denghai 618(DH618), Dika 653(DK653) and Yudan 9953(YD9953), were selected in the field experiment in the middle reaches of Yangtze River(Jingmen, Hubei) in 2019. They were successively sown as spring maize and summer maize, and were mechanically harvested at physiological maturity(T1), 7 d(T2) and 14 d(T3) after physiological maturity, respectively. The differences in yield, grain dehydration dynamics, mechanical harvest quality and its response to delayed harvest between spring maize and summer maize were analyzed. Regression analysis was used to study the main influencing factors for the gain broken rate and the relationship between grain dehydration and the accumulated temperature after silking(GDD_{≥10 ℃}). 【Result】The results showed the meteorological conditions during the plant growing season were different between SP and SM. The SP had longer growth period, more dry matter accumulation than that of SM. The average yield of three varieties in SP was significantly higher than that of SM with average increase of 64.6%(P<0.05, the same below). The impurity ratesin SP and SM were all lower than 3.00%. However, the grain broken rate and loss rate were all higher, which were the main problems in maize mechanical harvest quality in this region. The grain water content of SP(15.7%-35.5%) was higher than that of SM(14.6%-21.5%), and remarkably dropped along with the delay in harvest. The grain broken rate of SP linearly increased with the increase of grain water content(R²=0.543, P=0.024), while the broken rate of SM showed a quadratic curve relationship with grain water content(R²=0.509, P=0.118). The grain volume of SP(0.27-0.36 cm³/grain) was greater than that of SM(0.19-0.32 cm³/grain), and there was a significant negative quadratic relationship between grain volume and the grain broken rate(R²=0.452, P=0.009). Both of SP and SM presented an obvious Logistic model linking the grain water content and the GDD_{≥10 ℃}. However, the responses of grain moisture dehydration to the GDD_{≥10 ℃}were quite different between SP and SM. When the grain water content decreased to the same level, the SP required more GDD_{≥10 ℃}than SM according to the logistic models.【Conclusion】The differences of meteorological conditions between SP and SM maize growing period resulted in significant differences in mechanical harvest yield, mechanical harvest quality and grain dehydration process in the middle reaches of the Yangtze River. Compared with SM, SP has longer growth period, higher biomass and yield, lower grain breakage rate, but has similar mechanical loss rate. In the middle reaches of the Yangtze River, delayed harvest has no obvious effect on the mechanical harvest quality of summer maize, but delayed harvest for about 7 d can effectively reduce the broken rate and loss rate in mechanical harvest of spring maize.